1. Field of the Invention
This invention relates to a color television camera, and more particularly to a television camera having a test pattern projector.
2. Description of the Prior Art
In color television cameras, red, green and blue monochromatic images are usually formed on three image pickup tubes and electrical signals corresponding to these monochromatic images are taken out. Thereafter, the electrical signals are subjected to an electrical processing and color signals are obtained through an encoder. With these color television cameras, the situation that the intensity of illumination of an object becomes insufficient usually does not occur under the sun light and therefore, they are designed so that the maximum sensitivity is obtained with an illumination having a color temperature of about 3000.degree. K. as the standard so as to enable the cameras to be most effectively used under an artificial illuminating source.
Where an object is illuminated by other illuminating light than 3000.degree. K. as in the outdoor environment, the camera is adjusted by a color temperature changing filter or painting as if the object were illuminated by an illuminating light of 3000.degree. K.
Therefore, even if the illuminating light source of the pattern projector is at 3000.degree. K., such light actually cannot be said to be an illuminating light of 3000.degree. K. due to this color temperature changing filter. Accordingly, where the color temperature changing filter is used or painting is effected, the color temperature of the illuminating light source of the pattern projector must be changed to the color temperature of the illuminating light of the object.
The chart illuminating system of the conventional television lens has been provided by a single lamp, but the characteristic of a tungsten lamp is such that if the lamp voltage is varied, not only the quantity of light but also the color temperature is varied at the same time and so, in order to obtain a desired characteristic of the television camera, it is necessary to adjust it by the use of an ND filter or a color temperature filter. However, the ND filter and the color temperature filter are not continuous and the resolving optical system and image pickup tubes of the television camera have irregularity and this leads to an excessive adjustment time required to obtain the required characteristic of the camera. Further, now that it has become possible to adjust the camera by the use of a computer, it becomes necessary, for example, to vary only the quantity of light without varying the color temperature for the chart and illuminating system of the lens or to provide an illuminating light source having the same color temperature as that of the color temperature filter of the television camera.